Sealing up the HVAC system

[black2002ls]

Our house was built in 96. It has an upflow furnace unit with a plenum in the attic. The ducts all appear to be rigid metal and wrapped in foil backed insulation. Just a quick inspection of the joints at the plenum, they all leak. The corners on the plenum are leaking as well. This leads me to believe that every joint in the system is leaking. It would also explain why there is little to no airflow at the far end of the house (in the bedrooms).

Has anyone rei sulated and sealed their ductwork? I am about to go pick up a tub of mastic and seal up everything at the plenum. I am wondering if I should plan to pull the old insulation, seal all of the joints and then re-insulate.

[BradM]

You should go to Home Depot and ask for "duct tape". Great stuff.

[Chuck_Finley]

Do not use duct tape. On any hvac type installs, make sure to use strictly a metal tape which you can actually find at Lowes. Shurtape is one brand I currently have. This is good for sealing plenum or fiberboard boxes, whatever. But if you're talking about sealing the joints on the sheet metal ducts themselves, then yes you want to use mastic. Make sure it's water based and sometimes you can also find this at Lowes too..Design Polymerics I believe is the brand name. As far as tearing off insulation, applying mastic, and then putting insulation back on...I'd make sure you can identify a leak somewhere first before going through all the effort. Perhaps the air flow is a little low? That might also be an indication of a leak.

[black2002ls]

Yes, airflow is low in every room but the family room. The unit is in a closet that backs up to the family room and the vent is fed by a short, small duct. It is the shortest run, so it makes sense that is gets the most airflow. Everything else is branched off of larger ducts. I checked a couple of places in the vacinity of duct joints, and I could feel air escaping the duct work.

I picked up a bucket of mastic and sealed up the plenum, as well the areas where the furnace and plenum meet.

There were a few areas near the plenum where the pinch seam in the ducts had a little bit of leakage.

So foil tape where sections of duct meet, and mastic in ardas that aren't designed to come apart?

I may contact my HVAC vendor and see if they can get a good price on new insulation. It isn't a large system. 3 lines coming from the plenum. One line that runs to the far end of the house and branches off for the 3 bedrooms and 2 bathrooms, one line that runs to the family room, and one line that branches for the utility room, kitchen, and breakfast nook.

[black2002ls]

Oh, and Duct Tape never crossed my mind! I spend a lot of time looking at HVAC system rough ins. I know better!

[8mpg]

like they said above... foil tape and lots of mastic. Redoing the insulation isnt going to be that cheap but getting to r8 could save money in the long term

[Swamp Donkey]

You might check the wiring on your blower, sometimes they are wired to the lowest speed setting. When I installed mine I wired it to the high setting because I prefer more airflow. Of course fix the leaks first!

[black2002ls]

You might check the wiring on your blower, sometimes they are wired to the lowest speed setting. When I installed mine I wired it to the high setting because I prefer more airflow. Of course fix the leaks first!

I plan to once it cools down. The existing insulation is stapled along the seam, so it may be pretty easy to pull it, seal it up, and reinstall the insulation